Process of silver coating plastic



June 8, 1954 J. s. JUDD 2,680,695

PROCESS OF SILVER COATING PLASTIC Filed oct. 12, 1948 IUVEH faz-75 dof/N (/ua Patented June 8, l1954 PROCESS OF SILVER COATING PLASTIC John S. Judd, Birmingham, Mich., assignor to Lyon, Incorporated, Detroit, Mich., a corporation of Delaware Application October 12, 1948, Serial No. 54,175

3 Claims.

This invention relates to a process of making a iiexible mirror and more particularly to a process of silver coating flexible plastic sheet to provide a flexible mirror.

An object of this invention is to provide an improved process of making a flexible plastic mirror which lends itself to economical production.

Another object of this invention is to provide a process of silver coating plastic sheet in such manner that the sheet may be readily bent into different shapes Without separating the silver deposit fro-m the plastic sheet.

Yet another object of this invention is to prorvide an improved process of protecting a silver deposit on a transparent flexible plastic sheet and of sealing over and beyond the edges of the deposit on the sheet.

Another object of this invention is to provide an improved flexible mirror with a protective coating on the mirrored deposit extending beyond the edges of the deposit on the carrier for sealing the edges of the deposit to the carrier.

In accordance with the general features of this invention there is provided in a process of making a mirror on a flexible sheet of transparent plastic material, the steps of first applying a silver coating to a portion of the surface of the sheet and thereafter applying over the coating, such as by spraying, a flexible lacquer to protect the silver deposit and to seal over and beyond the edges of the same on the plastic sheet.

A further feature of the invention resides in the use of a protective coating, such as a copolymer of butadiene and styrene, which has the characteristic of iirmly adhering, upon drying, to the silver deposit and plastic and which will flex without rupture with the plastic sheet.

Other objects and features of the invention will more fully appear from the following detailed description taken in connection with the accompanying drawing which indicates a single embodiment thereof and in which:

Figure 1 is a diagrammatic front View of a transparent ilexible plastic mirror made in aclcordance with the features of this invention;

Figure 2 is a rear View similar to Figure 1 partly broken away and showing the protective lacquer over the silver deposit and beyond the edges of the same and sealing off the edges of the deposit onto plastic; and

Figure 3is a fragmentary cross-sectional view taken on substantially the line III-III of Figure 2, looking upwardly.

As shown on the drawings:

The reference character I designates generally a thin exible sheet, which may be of any suitable shape or size, and preferably comprises a sheet of conventional thin transparent resiliently flexible plastic resin. For example, ther-- be used. Such plastic resins are well known in the art and when in sheet form are resiliently iiexible Without rupture.

I propose in accordance with the features of this invention to use such a sheet of transparent plastic material as the carrier for a mirror of silver deposit II which may be of any suitable shape or extent but is preferably of an area less than that of the surface of the sheet so that a portion of the sheet extends beyond the deposit on all sides of the same, as shown at -I2 in Figure 2.

In order to protect this mirror or silver deposit I I the entire sheet is coated with a exible lacquer I3 which extends beyond the edges of the deposit I I onto the plastic I2, as shown at I5 in Figure 3. Thus I am enabled to use this lacquer not only to protect the deposit but also to seal off the edges of the deposit on the plastic sheet. I have attained excellent results by using a lacquer such as one prepared with a styrene-butadiene water emulsion as a base and pigmented black. This lacquer is sometimes referred to as a copolymer of butadiene and styrene.

I shall list hereinbelow some of the specific solutions and values used in one successful embodiment of my invention but it is, of course, to be understood that my invention is not to be limited thereby.

First I shall enumerate hereinbelow some of the solutions that I have used and with which I have attained particularly good results in practicing my invention.

Silver nitrate: One gram per 100 cc. distilled water with a few drops of nitric acid to prevent hydrolysis.

Sugar solution:

Distilled water 700 cc. Granulated sugar gm.

All of the above solutions Work best at a temperature cf about 20 C.

Tin chloride solution: cc. of a concentrated 'solution of tin chloride diluted to 1,000 oo jv In practicing my invention I have used a number of diiferent commercial types of plastic resins including thermoplastic resins. A typical illustration is cellulose acetatebutyrate. 'Ihe lsheet the: silvering. solution yon it. Letfthis stand for l f'minutesf thenpour 'it-"off 'and' rinse with v distilled Water.

7. Amiirror withgreater` brilliance/'is achieved byndepositing; afsecond coating. This-is vdone by repeating step #6.

8. ,The .silveringfsolution:isxprepared as follows:

(a) To 100 cc. oirtheisilver-nitrate solution ladd dilute ammonia drophy drop until theirst precipitate Whicliiorms, almost disappears.

(b) Addv 50 cc. of the potassium hydroxidesolution with stirring.

(c) Add dilute ammonia again-drop by drop until `the precipitate almost disappears.

(d) Tothe above,Vv add about 1/ 15 of its'volume of the sugar solution andstir.

(e) i Pour the silveringV Asolution thus prepared rapidly on the plastic.

9. After mirroring :and rinsing, the mirror may .be vair dried enforce dried in an oven -at 188 F.

l0. To protect the silver from rubbing ofi, spray with atype of coating `which will not adversely ailect the plastic. l@ne-type of protective coating I' have yused successfully isa Vpigmentedabritadiene styrene lacquer ofthe character-previously alluded to.

il. -Aiteispraying the coatingimay be air-...dried ror 4iorce driedin an oven at 180 F.

Afterthe silveredor mirrored sheethas-been dried, it can be readily bent intoranyshape, such for example, Yasi a cylindrical shapewithout rupturi-ngfor.fracturingthe coating thereon. `Such a mirrored sheet may-be used; forexainple, as a covering for a column where it :is desired-to ornament the column. It may also be used. to advantage' curved'shoiv cases and forv ornamental and'display purposes.

it will he appreciated that'only a very small,

margin of the sheet need be left uncoated with silver, asthe vportionleit unsilvered need only be sufficient for a'bond with .the protective coating beyond'the edge of the deposit. VThis-feature `is advantageous'as it minimizes thelikelihood of the silver coating becoming separated from thel plastic ron' bending oi" thefplasticand also 'enables complete sealing vofthe'silver Adeposit.

It will, oi course,-be understood that various details of construction mayl lie-'variedthrough a Wide range Without departing from the'principles` of this invention:andl it is; therefore, `not the purpose to limit the patent-'grantedhereon otherwise than"necessitatedsby; theffscope :off-they appended claims.

I claim as my invention:

l. In aprocessofmaking `aflexibler:mirror-'on a iexibleplastic resin sheet, thesteps-ordnet l soaking Y a transparent .-Water-,absorptivef plasticV sheet in distilled Water until the sheet absorbs some Water on its surface, cleaning the sheet by scrubbing/'the same with a-gpotassium hydroxide vsolution, then rinsingfthehsheet successively in distilled water and a tin chloride solution, then laying the sheet out in substantially flat form, pouring. a silvering solution on a portion of the sheet to be silvered to eiiect precipitation of a `'metallic silver-deposit thereon, pouring o excess .solutionafter the deposit has formed, rinsing thefsilvered-sheet with distilled water, depositing `a ,secondcoatotmetallic silver on the previous deposit by again pouring a, silvering solution on theprevious deposit on the sheet to effect precipitation of a second metallic silver deposit :thereon and again f rinsing with distilled water, drying the silverY coated sheet andv then spraying lvover :the silver deposit. andbeyond the: margin of the deposit onto the plastic sheeta coating of iexilole butadienefstyrene copolymer A.lacquer to fprotectthesilvervdeposit andto -seal over fand beyond the` ledges; of-,the :same ontov plastic-sheet.

2. In a process of making a flexible mirror. on Va -iiexible plastic resinrsheet, the/steps zof rst soaking a transparent waterfabscrptive:plastic Vsheet in dstilled'fwater until the sheetabsorhs some -Water :on itssuriace-cleaning the sheet by scrubbing the samefwith a potassium hydrox- `idesolution, tifienKr-insing the'sheet successively -in .distilledwater-and a tinchloridesoiution, then klaying -the sheet outin substantially flatform, pouring .a vsilvering solution ;onaportion 4of the sheet to be silvered to form a; `metallic silver de :posit thereon, i pouring 1 cli excess solution after the deposithasjiorined,*rinsing thesilvered sheet .with distilled water, depositing` asecond-coat of metallic `silver fon theV previous deposit by yagain :pouring-a silvering-solution onthe previous -derposit= on the sheetytofeiiectprecipitation of a second metallic silver deposit thereon and again rinsing- Withfl distilled .-vvaterg` drying the Asilver coated sheet yand thenfspraying over the silver -.-deposit =and beyondthe margin .of the deposit -onto .the `plastic sheet a coating offlexible llac- .quer of a. copolymer :of butadiene and styreneto .protect the.silvertdepositmandfto seal over and -beyondthe edges-o thesame'ontoY plastic sheet.

3. In. ,a process oi` makingf al. iexible Water- .absorptive .-inirror- =on-a ilexibletransparentplas- (tic tresi-n sheet.- the fstepsf of firstA soaking l the vplastic isheet vin--vvater until the Vsheet Y absorbs :some wateren itssurface-cleaning the sheetwith a potassium :hydroxide solution, then rinsing thegsheetfsuccessively water-aandA a tin vchlo- .ridef-solution, then laying; the 4.sheet out-in subfstantially;-flatform -depositing .by chemicalv l.prezzcpitationa. metallic silver Ycoating from aV silvering solution on awportioniof'- thefsheet to beisilvered, f-pouring.; ont: excess.l solution. after.- thev ,de-

posit has ffset, `rinsing the l.silvered :sheet .With Water,..andA then: applying :oven the :silver vdeposit the sil-ven deposit.

.References Cited'- linithe ffile Tof 'this jpatent l UNIT-ED. ,STATES PATENTS 

1. IN A PROCESS OF MAKING A FLEXIBLE MIRROR ON A FLEXIBLE PLASTIC RESIN SHEET, THE STEPS OF FIRST SOAKING A TRANSPARENT WATER-ABSORPTIVE PLASTIC SHEET IN DISTILLED WATER UNTIL THE SHEET ABSORBS SOME WATER ON ITS SURFACE, CLEANING THE SHEET BY SCRUBBING THE SAME WITH A POTASSIUM HYDROXIDE SOLUTION, THEN RINSING THE SHEET SUCCESSIVELY IN DISTILLED WATER AND A TIN CHLORIDE SOLUTION, THEN LAYING THE SHEET OUT IN SUBSTANTIALLY FLAT FORM, POURING A SILVERING SOLUTION ON A PORTION OF THE SHEET TO BE SILVERED TO EFFECT PRECIPITATION OF A METALLIC SILVER DEPOSIT THEREON, POURING OFF EXCESS SOLUTION AFTER THE DEPOSIT HAS FORMED, RINSING THE SILVERED SHEET WITH DISTILLED WATER, DEPOSITING A SECOND COAT OF METALLIC SILVER ON THE PREVIOUS DEPOSIT BY AGAIN POURING A SILVERING SOLUTION ON THE PREVIOUS DEPOSIT ON THE SHEET TO EFFECT PRECIPITATION OF A SECOND METALLIC SILVER DEPOSIT THEREON AND AGAIN RINSING WITH DISTILLED WATER, DRYING THE SILVER COATED SHEET AND THEN SPRAYING OVER THE SILVER DEPOSIT AND BEYOND THE MARGIN OF THE DEPOSIT ONTO THE PLASTIC SHEET A COATING OF FLEXIBLE BUTADIENE-STYRENE COPOLYMER LACQUER TO PROTECT THE SILVER DEPOSIT AND TO SEAL OVER AND BEYOND THE EDGES OF THE SAME ONTO PLASTIC SHEETS. 